Inspection chambers are required to be provided in sanitary sewer systems in many jurisdictions. An inspection chamber is typically installed where the sanitary sewer outlet from a building joins the sewer main of a municipal sewer system. Inspection chambers serve two main purposes. First, during construction of a new sewage system an inspection chamber can be used as a location for a plug to seal the passage between the new sewage system and the sewer main until the new sewage system has been tested and approved. After testing and approval, the plug can be removed by hooking a handle on the plug and pulling the plug out of the inspection chamber. Second, an inspection chamber can be used as a point of access to remove blockages from a sewer system.
An inspection chamber is typically installed at least several feet underground. The inspection chamber typically has interior dimensions slightly larger than the diameter of the sewage outlet pipe in which it is installed. Typical diameters of sewage outlet pipes from residential or light industrial buildings are in the range of 4 inches to 6 inches. A generally vertical access pipe, which is typically somewhat larger in diameter than the sewage outlet pipe, extends from the inspection chamber to the surface where it is sealed with a cap. The access pipe is typically several feet long. Typical diameters of access pipes are in the range of about 6 inches to 10 inches. After an inspection chamber has been installed it is very difficult to gain access to the inside of the inspection chamber.
It is generally desirable to provide a back-flow valve in the sewage outlet pipe. A back-flow valve serves to prevent sewage from backing up from the municipal sewer into a building. The back-flow valve also serves to prevent vermin, such as rats, from entering a building from the municipal sewer lines through the building's sewage outlet pipe. A problem with back-flow valves is that they are installed in the sewage outlet line which is several feet underground. If the back-flow valve malfunctions or if debris gets stuck in the back-flow valve then it is generally necessary to dig down to the back-flow valve to replace or repair it. This is both disruptive and expensive.
The inventors have recognized a need for an inspection chamber which can be plugged, as described above, during testing and approval of a sewage system and has an integral back-flow valve. It has not been previously practical to provide such an inspection chamber because any back-flow valve would interfere with insertion or removal of a plug. After the plug has been removed the inspection chamber is several feet down the access pipe and is not easily accessible.